Marlin 1.1 Z-Homing to Probe lowers bed before raising.

Hi Everyone,

My CoreXY machine has been dormant for almost a year until this week when I brought her back to service. In the process I upgraded the Marlin Firmware to 1.1 and it appears there is a new Z-axis homing process.

The new process should raise the bed up quickly until the probe is tripped, lower a bit then raise more slowly until probe trips, and then it lowers a bit. The problem I have is that when I first turn my machine on the bed is resting at the bottom of the "cube". When the Home Z command fires the cpu tries to lower the bed (i'm guessing) 10-15mm which results in a loud clacking sound because it can't go lower. Then it raises it and homes just fine.

I've scoured the configuration.h file but can't find any logic that would related to "lower before homing" or something of the like... Any clue where this behavior can be changed and/or what's causing it?

Any help would be awesome! (i've attached the config as well in case that helps)

Cheers~

Andy

Maybe this behaviour is implemented in the G28 for CoreXY command lines?
Try searching for G28 in the whole Marlin1.1 code and see what you find.
Or raise your printer bed position before sending a G28.

G92 X... Y... Zmax_z
G91
G0  Z-20
G90
G28

Thank you very much for your reply.

A little more testing and it seems that when I issue a "Home X" command G28 X the bed goes down... I'm suspecting something related to the new "safe-homing" feature so I'll be digging through that.

I have corrected this behavior but it does leave a bit of danger in the equation.

While I understand what this is supposed to protect against IE keeping the printhead clear of the bed when homing this is problematic on my CoreXY where the bed(z-axis) rests at the bottom of the cube.. Hence when I issue G28 it tries to move lower to make room for the X homing cmd. For now these are all staying at 0... If anyone has a suggestion on how to set this up better for the CoreXY use case please chime in.

All of the parameters below had to be changed to 0

#define Z_CLEARANCE_DEPLOY_PROBE 10 // Z Clearance for Deploy/Stow
#define Z_CLEARANCE_BETWEEN_PROBES 5 // Z Clearance between probe points

// For M851 give a range for adjusting the Z probe offset
#define Z_PROBE_OFFSET_RANGE_MIN -20
#define Z_PROBE_OFFSET_RANGE_MAX 20

#define Z_HOMING_HEIGHT 4


Also, if you're using earlier versions of Marlin it seems there have been some name changes Z_Clearance.. used to be something like Z_height.. so it took a while to dig through.

Hope this helps someone else!